Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 1Citation - Scopus: 1Type-3/2 Seesaw Mechanism(American Physical Society, 2021) Demir, Durmuş Ali; Karahan, Canan; Sargın, OzanThe type-I seesaw mechanism provides a natural explanation for tiny neutrino masses. The right-handed neutrino masses it requires are, however, too large to keep the Higgs boson mass at its measured value. We show that vector spinors, singlet leptons that are like right-handed neutrinos, generate tiny neutrino masses naturally through the exchange of spin-1/2 and spin-3/2 components. This one-step seesaw mechanism, which we call the type-3/2 seesaw, keeps the Higgs boson mass unchanged at one loop and gives cause therefore to no fine-tuning problem. If the on-shell vector spinor is a pure spin-3/2 particle, then it becomes a potential candidate for hidden dark matter which gets diluted due only to the expansion of the Universe. The type-3/2 seesaw provides a natural framework for the neutrino, Higgs boson, and dark matter sectors, with overall agreement with current experiments and observations.Article Citation - WoS: 4Citation - Scopus: 4Hidden Spin-3/2 Field in the Standard Model(Springer Verlag, 2017) Demir, Durmuş Ali; Karahan, Canan; Korutlu, Beste; Sargın, OzanHere we show that a massive spin-3/2 field can hide in the SM spectrum in a way revealing itself only virtually. We study collider signatures and loop effects of this field, and determine its role in Higgs inflation and its potential as dark matter. We show that this spin-3/2 field has a rich linear collider phenomenology and motivates consideration of a neutrino–Higgs collider. We also show that the study of Higgs inflation, dark matter and dark energy can reveal more about the neutrino and dark sector. © 2017, The Author(s).Article Citation - WoS: 2Citation - Scopus: 2Higgsed Stueckelberg Vector and Higgs Quadratic Divergence(Elsevier Ltd., 2015) Demir, Durmuş Ali; Karahan, Canan Nurhan; Korutlu, BesteHere we show that, a hidden vector field whose gauge invariance is ensured by a Stueckelberg scalar and whose mass is spontaneously generated by the Standard Model Higgs field contributes to quadratic divergences in the Higgs boson mass squared, and even leads to its cancellation at one-loop when Higgs coupling to gauge field is fine-tuned. In contrast to mechanisms based on hidden scalars where a complete cancellation cannot be achieved, stabilization here is complete in that the hidden vector and the accompanying Stueckelberg scalar are both free from quadratic divergences at one-loop. This stability, deriving from hidden exact gauge invariance, can have important implications for modeling dark phenomena like dark matter, dark energy, dark photon and neutrino masses. The hidden fields can be produced at the LHC.Article Citation - WoS: 16Citation - Scopus: 16Stop on Top: Susy Parameter Regions and Fine-Tuning Constraints(American Physical Society, 2014) Demir, Durmuş Ali; Ün, Cem SalihWe analyze minimal supersymmetric models in order to determine in what parameter regions with what amount of fine-tuning they are capable of accommodating the LHC-allowed top-stop degeneracy window. The stops must be light enough to enable Higgs naturalness yet heavy enough to induce a 125 GeV Higgs boson mass. These two constraints imply a large mass splitting. By an elaborate scan of the parameter space, we show that the stop-on-top scenario requires at least ΔCMSSM≃O(104) fine-tuning in the constrained minimal supersymmetric Standard Model (CMSSM). By relaxing the CMSSM parameter space with nonuniversal Higgs masses, we find that ΔNUHM1≃O(104). The CMSSM with a gravitino lightest supersymmetric particle works slightly better than the nonuniversal Higgs mass model. Compared to all these, the CMSSM with μ<0 and nonuniversal gauginos yields a much smaller fine-tuning Δμ,g≃O(100). Our results show that the gaugino sector can pave the road toward a more natural stop-on-top scenario.Article Citation - WoS: 7Citation - Scopus: 8Search for Gauge Extensions of the Mssm at the Lhc(American Physical Society, 2009) Ahmed, Ali; Demir, Durmuş Ali; Frank, Mariana; Turan, İsmailThe extensions of the minimal supersymmetric model (MSSM), driving mainly from the need to solve the μ problem, involve novel matter species and gauge groups. These extended MSSM models can be searched for at the LHC via the effects of the gauge and Higgs bosons or their fermionic partners. Traditionally, the focus has been on the study of the extra forces induced by the new gauge and Higgs bosons present in such models. An alternative way of studying such effects is through the superpartners of matter species and the gauge forces. We thus consider a U(1)′ gauge extension of the MSSM, and perform an extensive study of the signatures of the model through the production and decays of the scalar quarks and gluino, which are expected to be produced copiously at the LHC. After a detailed study of the distinctive features of such models with regard to the signatures at the LHC, we carry out a detailed Monte-Carlo analysis of the signals from the process pp→nleptons+mjets+E T, and compare the resulting distributions with those predicted by the MSSM. Our results show that the searches for the extra gauge interactions in the supersymmetric framework can proceed not only through the forces mediated by the gauge and Higgs bosons but also through the superpartner forces mediated by the gauge and Higgs fermions. Analysis of the events induced by the squark/gluino decays presented here is complementary to the direct Z′ searches at the LHC.